1. Field of the Invention
The present invention relates to image reading apparatuses, in which an original on a transparent original reading plate is read through this original reading plate, and image forming apparatuses provided with these.
2. Description of the Related Art
This type of image reading apparatus reads images of originals and is also referred to as a scanner, and is used independently or equipped in a copier or the like. When used independently, an image of the original that has been read is outputted to an external printer or the like, and when used equipped in a copier, the image of the original that has been read is reproduced by the copier.
This image reading apparatus is provided with a transparent original reading plate on which an original is placed, an illumination portion that illuminates the original through the original reading plate, and a reading portion that reads the original through the original reading plate. The original reading plate is a glass plate or the like. For example, the illumination portion has a plurality of light-emitting elements provided in rows, and the rows of the light-emitting elements are arranged along a direction (main scanning direction) in which the reading portion scans, and light from the light-emitting elements is irradiated onto the original through the original reading plate. The reading portion has a line sensor such as a CCD arranged along the main scanning direction, and light reflected by the original is incident on the line sensor through the original reading plate such that the original is read by the line sensor.
For example, the illumination portion and the reading portion are arranged below the original reading plate, and while the original is transported in a sub scanning direction on the original reading plate, light from the light-emitting elements of the illumination portion is irradiated onto the original and the original is read repetitively in the main scanning direction by the line sensor.
Incidentally, sometimes paper dust of the original adheres to a surface of the original reading plate. When paper dust is left on the surface of the original reading plate, the reading portion repetitively reads the paper dust of the surface of the original reading plate along with the original, and streaks are produced that extend in the sub scanning direction on the image that is read by the reading portion, then these streaks appear on the reproduced original. For this reason, when users or service personnel discover streaks on the reproduced originals, the surface of the original reading plate is cleaned with a cloth to remove the paper dust.
Furthermore, in JP 2002-258545A for example, a cleaning roller is arranged on a contact glass (corresponding to the original reading plate), and a cleaning portion and a reflective portion are provided at a peripheral surface of the cleaning roller. During reading of the original, the reflective portion of the cleaning roller is faced toward the contact glass, then while the original is passed between the contact glass and the cleaning roller, the original is illuminated by the lamp through the contact glass, and the original is read by the line sensor. Furthermore, when carrying out reading using the line sensor without causing the original to travel, artifacts on the surface of the contact glass are detected and the cleaning roller is caused to rotate to clean the surface of the contact glass using the cleaning portion of the cleaning roller.
However, when detection of paper dust on the surface of the original reading plate is dependent on the discovery of streaks on the reproduced originals by a user or service personnel, sometime this discovery is delayed and streaks are produced on a great number of reproduced originals.
Furthermore, in a case where uniform illumination is carried out using a lamp and artifacts on the contact glass are detected using a line sensor as in the foregoing JP 2002-258545A, the artifacts can be detected without problem as long as the artifacts are ink, but when the artifacts are paper dust, detection of paper dust is difficult since paper dust is white and the background of locations for reading the original are also white. Further still, a cleaning roller and a drive mechanism thereof are required, which increases the number of components and makes the configuration more complicated.